Major US wireless carriers are gearing up to shut down their old 3G networks — a process that has been fraught with delays and miscommunication as companies alert customers with older phones that it’s time to upgrade. To that end, Verizon and AT&T have published guides to which devices will stop working after their 3G networks go offline next year. Here’s what you need to know.

Verizon has delayed its CDMA 3G network shutdown several times but is now firmly committed to shutting the network down by December 31st, 2022. All 3G basic phones and smartphones will lose service, but some 4G devices will be impacted as well — namely, those that don’t support VoLTE (Voice over LTE). A few connected devices are affected, too; take a look at Verizon’s full guidelines for more details.

Taking the opposite approach, AT&T has published a complete list (spotted by XDA Developers) of exactly which phones, tablets, and smartwatches will keep working after its 3G shutdown on February 22nd, 2022. (Separately, there’s concern in the alarm industry: many home security devices use AT&T’s 3G and it’s possible that users won’t be able to replace them in time.) In any case, AT&T makes it easy to understand which mobile devices will keep functioning after the network shutdown.

T-Mobile’s 3G shutdown is a bit more complicated. It operates a UMTS 3G network, which the company will reportedly shut down in April 2022, and Sprint’s former CDMA 3G network, which the company says it will sunset on January 1st, 2022. T-Mobile hasn’t published a list of affected devices, but customers can check their device’s IMEI to see if it’s LTE and VoLTE compatible, which should indicate whether the device will keep working after the 3G networks are taken offline.